Turbocharged engine systems may use low-pressure cooled exhaust gas recirculation (EGR) systems which direct exhaust gas from downstream of a turbo turbine and inject the exhaust gas upstream of the turbo compressor.
For example, low-pressure EGR systems may be used on boosted engines to increase fuel economy via reduced pumping losses, increase combustion efficiency, and reduce engine knock tendencies. Further, low-pressure cooled EGR systems may also be used on diesel engines to reduce emissions of nitrogen oxides (NOx) while increasing fuel economy via an increased cooling performance and turbo efficiencies compared to traditional “high pressure” EGR systems.
Additionally, in some examples, engines with EGR systems may include twin turbochargers where each turbocharger includes a compressor arranged along separate air intake passages of the engine. For example, one approach for a V-type engine with twin turbochargers is to provide a low-pressure EGR system for each turbocharger.
However, the inventors herein have recognized issues with approaches which utilize separate low-pressure EGR systems for each turbocharger in a twin turbocharged engine. For example, using separate EGR systems may result in dual sets of EGR components and sensors leading to increased cost, packaging issues, and an increase in engine control complexity. For example, imbalances in such a configuration may increase complexity of controlling two EGR valves to achieve the same EGR rate on each bank of the engine. Further, such approaches may result in negative interactions between lubrication oil in positive crankcase ventilation (PCV) gases and the EGR system, resulting in potential EGR valve and compressor wheel contamination risks, for example.
As one example, the above issues may be addressed by a system comprising a first turbocharger in a first intake passage with a low-pressure EGR system fluidically coupling engine exhaust exiting the first turbocharger turbine to engine intake air entering the first turbocharger compressor, and a second turbocharger in a second intake passage without a low-pressure EGR system fluidically coupling engine exhaust exiting the second turbocharger turbine to engine intake air entering the second turbocharger compressor.
In this way, the number of components and sensors used in the EGR system may be reduced leading to decreased cost. Further, greater flexibility in packaging of low-pressure EGR systems may be achieved and engine control complexity in operating the EGR system may be reduced. Additionally, in such a configuration, a positive crankcase ventilation (PCV) system can be coupled to the engine bank which does not include a low-pressure EGR system which may result in reduced EGR valve/compressor contamination. Further advantages may include an increased low-pressure EGR flow capability by utilizing natural bank-to-bank imbalances to decrease exhaust back-pressure, for example, thus enabling improved fuel economy and reduced exhaust gas emissions, such as NOx.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.